For overhead pipeline, guided wave testing (GWT) was used to detect the severe corrosion under insulation.

1. Guided Wave Testing on Insulated
Overhead Pipeline Corrosion
Lee Ping Hung
Taiwan Metal Quality Control Co. Ltd
Tel. 07-8019312, 8019340 Fax. 07-8063017
WEB: www.tmqc.com.tw
1 2016/10TMQC in CNDT2016

2. Guided Wave Testing, GWT
GWT Ring
Pipe corrosion
2016/10TMQC in CNDT20162
Local Corrosion
General Corrosion

3. Guided Wave Propagation Beyond Elbow
2016/10TMQC in CNDT20163
T(0,1)
Incident
T(0,1)
Focusing
T(0,1)
Reflection
T(0,1)
Transmission
T(0,1)
Reflection
T(0,1)
Mode Conversion

4. Guided Wave Testing on Insulated Overhead
Pipeline Corrosion
2016/10TMQC in CNDT20164
 Testing on both vertical
section
 Testing on Horizontal section

5. GWT signals of pipe support beyond the
elbow on overhead pipeline
2016/10TMQC in CNDT20165

6. Wave Propagation at Pipe Support and Elbow
2016/10TMQC in CNDT20166
Reflection
Transmission
Wave Leakage
Pipe Support Pipe Elbow
Wave Natural Focusing

7. Research in 2012 CNDT conference
2016/10TMQC in CNDT20167
Frequency: 20~30kHz
-Guided Wave Focusing
-Sensitivity higher than 2~3 times
Easy to miss
corrosion detection
Natural focusing is depended on
the wave mode, frequency and
location
According to the difference of the
sensitivity, it needs modify the
severity of the GWT signal.
Next Step：How to get a
reliable analysis beyond elbow

8. 2014
Guided wave natural focus map at elbow
2016/10TMQC in CNDT20168
Intrado
Extrado

9. 2014
Guided wave natural focus map beyond elbow
2016/10TMQC in CNDT20169
Extrado
Intrado3 o’clock
9 o’clock

10. 2014
Guided wave natural focus map beyond elbow
2016/10TMQC in CNDT201610
3 o’clock
9 o’clock

11. GWT signal of Overhead Pipeline without
Corrosion
2016/10TMQC in CNDT201611
-25.0 -20.0 -15.0 -10.0 -5.0 0.0
0.0
0.5
1.0
1.5
2.0
2.5
-25.0 -20.0 -15.0 -10.0 -5.0 0.0
0.0
0.5
1.0
1.5
2.0
2.5
Distance (m)
B3W2S1W1B2B1
B4B3W2S1W1B2

12. GWT signal of Overhead Pipeline with
Corrosion
2016/10TMQC in CNDT201612
-20.0 -15.0 -10.0 -5.0 0.0
0.0
1.0
2.0
3.0
-20.0 -15.0 -10.0 -5.0 0.0
0.0
1.0
2.0
3.0
Distance (m)
-F1B5 B6X1 W3
B8-F1B7X2X3W3B6

13. Multi-frequency Analysis: GWT signal of
Overhead Pipeline with Severe Corrosion
2016/10TMQC in CNDT201613
-12dB
-14.0 -12.0 -10.0 -8.0
12
9
6
3
12
Clock
-14.0 -12.0 -10.0 -8.0
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Distance (m)
B6 X1 W3
-12dB
-14.0 -12.0 -10.0 -8.0
12
9
6
3
12
Clock
-14.0 -12.0 -10.0 -8.0
0.0
1.0
2.0
3.0
Distance (m)
Amp(Linear)
B6 X1 W3
45kHz 30kHz

14. GWT signal collected from the ring location
on horizontal section
2016/10TMQC in CNDT201614
-18dB
-4.0 -2.0 0.0 2.0 4.0 6.0
12
9
6
3
12
Clock
-4.0 -2.0 0.0 2.0 4.0 6.0
0.0
2.0
4.0
6.0
8.0
10.0
12.0
Distance (m)
Amp(Linear)
B7X2X3W3X1B6
Bottom
Corrosion

15. Corrosion X1,X2 surface VT after polishing
2016/10TMQC in CNDT201615
X1
Multiple holes
X2
Multiple severe corrosion

16. Conclusion
Pipeline Type
Simple support √ x
Welded support √ √
Clamp support √ √
Simple support √ x
Welded support √ √
Clamp support √ ∆
2016/10TMQC in CNDT201616
√: Need GWT，x: No need GWT，∆: Depend on contact condition
PS. If testing results on vertical section show obvious corrosion signal, another testing
location should be done in the overhead pipeline inspection results
Bare
Overhead
Pipeline
Insulated
Overhead
Pipeline
Pipe Support Type
Testing on both
vertical section
Testing on
Horizontal section